The present invention relates to semiconductor devices. More particularly, the invention relates to semiconductor devices having low band-to-band tunneling.
Band-to-band (BTB) tunneling describes the effect of electrons traveling from the valence band through a bandgap to the conduction band of a semiconductor device. As semiconductor devices get smaller, BTB tunneling increases due to higher doping levels, and more recently, through the use of narrow-bandgap materials Conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) include a channel region between a source and a drain that is pure silicon. This mitigates BTB tunneling because silicon has a relatively wide bandgap, but may also limit semiconductor performance. To increase the performance of a product, some conventional devices employ a channel region of strained silicon-germanium between the source and drain. However, this approach may increase the total amount of BTB tunneling in the integrated circuit due to the narrower bandgap of silicon-germanium, especially under compressive strain. The BTB tunneling is particularly egregious for high-voltage devices such as, for example, 1.8V devices for IO applications, which have a channel length much longer than the minimum lithographic capability.